1. Field of the Invention
The present invention relates to a variable speed change gear used for various machines requiring transmission of power, such as transportation machines including an automobile.
2. Description of the Related Art
At present, a variable speed change gear used for an automobile generally uses a metallic belt and a pair of pulleys. In the variable speed change gear of this type, the radius of the belt passed around the pulleys is changed to change the speed by continuously changing the groove width of each pulley. However, a structure which transmits power by means of a frictional force between the belt and the pulley has a problem in that the power transmission efficiency is decreased by the slip of belt, so that the whole of equipment must be made large to transmit high power.
To solve this problem, there has been known a variable speed change gear capable of transmitting power efficiently without the use of a belt and pulleys. For this type, a plurality of eccentric rotating bodies is provided between an input shaft and an output shaft disposed coaxially with each other. The eccentric rotating bodies are capable of being eccentric in the radial direction with respect to the input shaft. The rotational force of an eccentric rotating body whose angular velocity is the lowest or the highest in the eccentric rotating bodies rotated by the rotational force of the input shaft side is transmitted to the output shaft side by a one-way clutch, by which the rotation ratio between the input shaft and the output shaft is changed according to the eccentricity of each eccentric rotating body. The variable speed change gear of this type has been disclosed in, for example, Japanese Patent Publication No. 5-46459.
Although various types have been contrived in terms of the power transmitting construction and the shape of the eccentric rotating body for the variable speed change gear constructed as described above, all types have a drawback of easy occurrence of vibrations during its rotation because an eccentric force is applied in the radial direction of the input and output shafts by the eccentric rotation. For this reason, this type can be only used in the case of small size and low rotation in which the effect of vibration can be neglected, and it is difficult to practically use this type because of its large vibration in an application, such as an automobile, which requires large size and high rotation.